N.O.V.A. should have the best looking trees, maybe also Ravensword and in some tracks Real Racing. Avatar also has some amazing looking levels: “Good graphics” are a matter of taste. For me, Fastlane and Real Racing still offer the best racing experience, because they are really fast, followed by Asphalt 5. Galaxy on Fire has the best graphics for a space shooter. Rolando 2 for the 2.5D platforming stuff. geoDefense for the retro neon look. Broken Sword for the point and click adventure genre. Skies of Glory for the flight simulator stuff.
I agree with post above. I would also add here Dungeon Hunter (by Gameloft). If You like landscapes, You may enjoy Skies of Glory - WWII flight simulator with giant free-roaming areas.
App info is currently processing and/or the app is not yet fully available for sale on the US App Store. How good are those trees
Red Conquest has some epic graphics. You can zoom in in this game, and even at maximum zoom, you don't see any pixel-edges!